Search PubMed⌕ Search

Biomedical subjects

Z Gregus

Publications and source records attributed to Z Gregus.

At least 37 records · Page 2Linked to original sources
PubMed1992

Effect of lipoic acid on biliary excretion of glutathione and metals.

Several metals are excreted in bile as glutathione complexes, and their biliary excretion is facilitated by increased hepatobiliary transport of glutathione. The present study analyzed the effect of lipoic acid (LA; thioctic acid; 37.5-300 mumol/kg, iv), an endogenous disulfide which can be reduced in vivo to a dithiol, on the hepatobiliary disposition of glutathione-related thiols and the biliary excretion of metals (10 mumol/kg, iv) in rats. Administration of LA enhanced the biliary excretion of reduced glutathione in a dose-dependent fashion. Despite increasing glutathione output, LA (150 mumol/kg, iv) did not increase, but rather decreased, the biliary excretion of methylmercury, cadmium, zinc, and copper, which are transported into bile in a glutathione-dependent manner, as indicated by a marked reduction in their biliary excretion after diethyl maleate-induced glutathione depletion. In contrast, biliary excretion of inorganic mercury, which is minimally affected by glutathione depletion, was dramatically enhanced (12- to 37-fold) by LA administration. Following injection of LA, the concentrations of endogenous disulfides in arterial blood plasma (e.g., cystine, glutathione disulfide, cysteine-glutathione, protein-cysteine, and protein-glutathione mixed disulfides) were considerably diminished, while the levels of endogenous thiols (e.g., glutathione and cysteine) were increased. This finding indicates that LA, probably after enzymatic conversion to dihydrolipoic acid, can reduce endogenous disulfides to thiols. It appears that LA induces the transport of glutathione into bile by the temporary formation of dihydrolipoic acid-glutathione mixed disulfide, which after being translocated into bile is cleaved to LA and reduced glutathione. Because the glutathione molecule thus transported into bile cannot complex metals at the thiol group, this might be the mechanism for the observed failure of the LA-induced increase in biliary excretion of glutathione to enhance the hepatobiliary transport of metals that are transported into bile as glutathione complexes (i.e., methylmercury, cadmium, zinc, and copper). The observations also raise the possibility that endogenous dihydrolipoic acid, by forming a stable complex with mercuric ion, may play the role of a carrier molecule in the hepatobiliary transport of inorganic mercury.

Animals↗
PubMed1992

Identification of the mixed disulfide of glutathione and cysteinylglycine in bile: dependence on gamma-glutamyl transferase and responsiveness to oxidative stress.

Biliary excretion of glutathione disulfide (GSSG) is used as an index of oxidative stress. Analysis of endogenous thiols and disulfides in rat bile by reverse phase high performance liquid chromatography with electrochemical detection revealed an unknown disulfide which eluted immediately after GSSG. This disulfide was tentatively identified as the mixed disulfide of glutathione (GSH) and cysteinylglycine (Cys-Gly), based on its coelution on a reverse phase column with the synthetic GS-Cys-Gly. GS-Cys-Gly was also detected in bile of other species. On analyzing species differences in biliary excretion of GSH-related thiols and disulfides, it was concluded that biliary excretion of GS-Cys-Gly was related to the excretion of both GSSG and Cys-Gly, which is formed from GSH by gamma-glutamyltransferase (gamma-GT)-catalyzed hydrolysis. Species with low hepatic gamma-GT (i.e., hamsters and mice) excreted little Cys-Gly in bile. These animals excreted negligible amounts of GS-Cys-Gly even when biliary excretion of GSSG was markedly increased by paraquat-induced oxidative stress. Rats and guinea pigs, which have high hepatic gamma-GT activities, excreted large amounts of both Cys-Gly and GS-Cys-Gly. Treatment of rats with acivicin, an inhibitor of gamma-GT, decreased the biliary excretion of both Cys-Gly and GS-Cys-Gly. Paraquat treatment of rats resulted in an increase in GSSG excretion with concomitant increase of GS-Cys-Gly excretion. Rabbits, which also have high hepatic gamma-GT activity, excreted little GS-Cys-Gly into bile.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1992

Marked interanimal differences in susceptibility of Sprague-Dawley rats to diquat-induced oxidative stress in the liver: correlation with hepatic uptake of diquat.

Biliary excretion of oxidized glutathione (GSSG) is used as an index of oxidative stress. We observed a marked interanimal difference in susceptibility to diquat-induced oxidative stress. When diquat injections (120 mumol/kg, i.v.) were administered to rats, a 60-fold increase in the biliary excretion of GSSG was observed in 40% of the rats (responders); however, diquat failed to increase the biliary excretion of GSSG in 60% of the animals (nonresponders). This interanimal variation is not due to differences in the hepatic metabolism or hepatobiliary transport of GSSG, as no interanimal difference was observed in the biliary output of GSSG after administration of another oxidative stress-inducing agent, t-butyl hydroperoxide (1.4 mmol/kg, i.v.). We then examined the hepatobiliary disposition of diquat (120 mumol/kg, i.v.) using a high-performance liquid chromatography procedure to quantitate diquat in blood, liver and bile. No differences in blood or biliary concentration of diquat were noted between responders and nonresponders. However, a marked difference was observed in the hepatic concentration of diquat in responders and nonresponders. The responders exhibited a 4-fold higher hepatic diquat concentration than the nonresponders (65 or 15 nmol/g, respectively) 30 min after diquat administration. In conclusion, this study demonstrates a marked interanimal variation in the susceptibility of Sprague-Dawley rats to oxidative stress produced by diquat, which appears to be due to interanimal difference in the hepatic accumulation of diquat.

Animals↗
PubMed1991

Glutathione-dependent biliary excretion of arsenic.

This study aimed to clarify whether glutathione (GSH) plays a role in the hepatobiliary transport of arsenic. For this purpose, the biliary excretion of 74As was measured in urethane-anaesthetized rats for 2 hr after the administration of labelled sodium arsenite (50 mumol/kg, i.v.) or arsenate (150 mumol/kg, i.v.) and under the influence of sulfobromophthalein (BSP), indocyanine green (ICG) or diethyl maleate (DEM) which are known to diminish hepatobiliary transport of GSH. Although the biliary excretion of arsenic was different after arsenite and arsenate administration in terms of quantity (19% vs 6% of dose in 2 hr, respectively) and time course, arsenic excretion responded similarly to BSP (50 mumol/kg, i.v.), ICG (25 mumol/kg, i.v.) or DEM (4 mumol/kg, i.p.) irrespective of the injected arsenical. Initially the biliary excretion of arsenic in rats with either arsenite or arsenate was significantly reduced, but then moderately increased by BSP and, more lastingly, depressed by ICG, whereas it was virtually abolished by DEM. The responses of arsenic excretion to BSP, ICG and DEM were related, both proportionally and temporally, to the effects exerted by these agents on the hepatobiliary transport of GSH, as assessed by the biliary excretion of non-protein thiols. These findings indicate that the biliary excretion of arsenic after the administration of either arsenite or arsenate is dependent on the hepatobiliary transport of GSH. Transport of arsenic as a GSH complex may account for the GSH dependence of biliary arsenic excretion.

Animals↗
PubMed1990

Effect of sulfhydryl-deficient diets on hepatic metallothionein, glutathione, and adenosine 3'-phosphate 5'-phosphosulfate (PAPS) levels in rats.

Low dietary concentrations of methionine and cysteine are known to decrease hepatic glutathione content. However, it is not known if restricting the dietary content of these sulfur containing amino acids also affects hepatic levels of adenosine 3'-phosphate 5'-phosphosulfate (PAPS), the cofactor for sulfation, or metallothionein, a protein rich in sulfhydryl groups. Rats were fed diets lacking cysteine and containing various concentrations of methionine (0.15, 0.3, or 0.6%) for 8 days. Control diet contained 0.3% each of methionine and cysteine. Hepatic glutathione levels were decreased approximately 75% in rats fed diets containing 0.15 or 0.3% methionine. In contrast, PAPS and hepatic metallothionein concentrations were not decreased by the low sulfhydryl diets. Additionally, rats on the various diets were challenged by the administration of ZnCl2 (3 mmol/kg. sc). In both control rats and rats maintained on sulfhydryl-deficient diets, ZnCl2 increased hepatic metallothionein to the same level. However, significantly lower levels of PAPS were observed after ZnCl2 in rats receiving sulfhydryl-deficient diets than in controls. In summary, restriction of dietary sulfhydryl markedly decreases the hepatic content of glutathione and has a minor effect on PAPS concentration, but does not decrease the basal hepatic concentration of metallothionein or its induction by ZnCl2.

Adenine Nucleotides↗
PubMed1989

Inducibility of glutathione S-transferases in hamsters.

The effects of 3-methylcholanthrene (3-MC), 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), phenobarbital, trans-stilbene oxide (TSO), pregnenolone-16 alpha-carbonitrile (PCN), dexamethasone, ethanol, isoniazid and butylated hydroxyanisole (BHA) on hepatic glutathione S-transferase (GST) activities toward six substrates were determined in hamsters. TCDD and 3-MC, which are comparatively poor inducers of GSTs in rats, were most effective in enhancing GST activities in hamster liver. In contrast, TSO, BHA and phenobarbital, which are very effective inducers of hepatic GSTs in rats and mice, were ineffective or poor inducers of GSTs in hamster liver. While dexamethasone increased some GST activities, treatments with PCN, ethanol and isoniazid were without effect. The findings indicate that not only the control activity but also the inducibility of hepatic GSTs are different in hamsters from those in other species.

Animals↗
PubMed1989

Biliary excretion of acetaminophen-glutathione as an index of toxic activation of acetaminophen: effect of chemicals that alter acetaminophen hepatotoxicity.

Acetaminophen (AA) is converted, presumably by cytochrome P-450, to an electrophile which is conjugated with glutathione (GS). AA-GS is excreted into bile, therefore the biliary excretion rate of AA-GS may reflect the rate of activation of AA in vivo. In order to test this hypothesis, the effect of agents capable of altering the activation of AA including cytochrome P-450 inducers and inhibitors, cobaltous chloride which decreases the amount of P-450, prostaglandin synthetase inhibitors (indomethacin and naproxen), antioxidants (butylated hydroxyanisole, alpha-tocopherol, ascorbic acid and ascorbic acid palmitate) and other chemicals known to decrease AA hepatotoxicity (dimethylsulfoxide and cysteamine), on the biliary excretion of AA-GS was studied in hamsters, the species most sensitive to AA-induced hepatotoxicity. The biliary excretion of AA-GS increased linearly up to 1 mmol/kg of AA i.v., but at higher dosages exhibited saturation kinetics. Dosages above 0.5 mmol/kg lowered hepatic GS concentration. Of the cytochrome P-450 inducers, 3-methylcholanthrene and 2,3,7,8-tetrachlorodibenzo-p-dioxin, increased the biliary excretion of AA-GS (2.9- and 3.2-fold, respectively) whereas ethanol and isoniazid did not affect it, and pregnenolone-16 alpha-carbonitrile tended to decrease it (43%). Phenobarbital tended to increase the biliary excretion of AA-GS, but not in a statistically significant manner. Several cytochrome P-450 inhibitors [metyrapone, 8-methoxypsoralen, 2-(4,6-dichloro-biphenyloxy) ethylamine, alpha-naphthoflavone and cimetidine] decreased the biliary excretion of AA-GS, although SKF 525-A and piperonyl butoxide did not. Cobaltous chloride decreased dramatically the biliary excretion of AA-GS.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetaminophen↗
PubMed1988

Effect of glutathione depletion on sulfate activation and sulfate ester formation in rats.

Sulfation of organic compounds requires activation of inorganic sulfate via formation of adenosine 3'-phosphate 5'-phosphosulfate (PAPS). Inorganic sulfate can be formed by sulfoxidation of cysteine, which can be derived from GSH. Thus, a decrease in hepatic GSH may impair formation of inorganic sulfate, the synthesis of PAPS, and the sulfation of chemicals. This hypothesis was tested by investigating the effect of GSH depletion on the levels of inorganic sulfate in serum and of PAPS in liver, and on the capacity to form the sulfate conjugate of harmol in rats. Phorone (2 mmol/kg, i.p.) decreased hepatic GSH (97%), serum inorganic sulfate (63%), and hepatic PAPS (48%). Diethyl maleate and vinylidene chloride (6 mmol/kg, each, i.p.) were less effective than phorone in decreasing GSH in liver and inorganic sulfate in serum, and they did not alter hepatic PAPS levels. Three hours after phorone treatment, the nadir of hepatic PAPS concentration, harmol was injected in order to assess sulfation in vivo. After administration of harmol (100 and 300 mumol/kg, i.v.), less harmol sulfate and more harmol glucuronide were found in the serum of phorone-treated rats as compared to control rats. At the higher dosage of harmol, phorone reduced the biliary excretion of harmol sulfate while increasing the biliary excretion of harmol glucuronide. These results indicate that severe GSH depletion decreases PAPS formation and sulfation of chemicals. However, an increase in glucuronidation may compensate for the impaired sulfation.

Animals↗
PubMed1988

Species variations in biliary excretion of glutathione-related thiols and methylmercury.

The biliary excretion of methylmercury is thought to be related to the biliary excretion of nonprotein thiols in rats. Species differences in biliary excretion of glutathione (GSH) and related thiols are unknown; therefore, the relationship between the biliary excretion of GSH-related thiols and methylmercury in five species was studied. The biliary excretion rate of GSH-related thiols and disulfides was 369, 192, 94, 50, and 19 nmol/min/kg for mice, rats, hamsters, guinea pigs, and rabbits, respectively. The main thiol in mouse, hamster, and rat bile was GSH, whereas guinea pig and rabbit bile contained mainly cysteinylglycine (Cys-Gly). The larger percentage of Cys-Gly in guinea pig and rabbit bile was correlated with their greater hepatic gamma-glutamyltranspeptidase (GGT) activity than that observed in the other species. The biliary excretion rate (nmol/min/kg) of methylmercury was approximately 0.8 in mice, rats, and hamsters compared to significantly lower rates in guinea pigs and rabbits (0.15 and 0.03, respectively). It is concluded that the species-specific composition of GSH-related thiols and disulfides in bile is related to species variations in hepatic GGT activity, and that the species variation in biliary excretion of GSH-related thiols does not entirely account for the species variation in methylmercury excretion, indicating other factors are also apparently involved in determining the rate of biliary excretion of methylmercury.

Animals↗
PubMed1988

Effect of butylated hydroxyanisole on hepatic glucuronidation and biliary excretion of drugs in mice.

Inhibition of glucuronidation by depletion of UDP-glucuronic acid from liver impairs the hepatobiliary transport of glucuronidated xenobiotics. However, it is not known if enhancement of hepatic glucuronidation increases the biliary excretion of these compounds. Therefore, the effect of treatment with butylated hydroxyanisole (BHA), which increases hepatic glucuronidation capacity, on the biliary excretion of compounds undergoing glucuronidation was studied in mice. BHA-feeding (1% for 10 days) increased hepatic UDP-glucuronic acid content by 240% and enhanced hepatic UDP-glucuronosyltransferase activities (expressed per kg body weight) toward valproic acid, phenolphthalein, iopanoic acid and bilirubin 220, 180, 120 and 60%, respectively. BHA treatment did not influence the biliary excretion of unmetabolized cholephils, phenol-3,6-dibromphthalein disulphonate and phenolphthalein glucuronide, but enhanced that of phenolphthalein (+108%), iopanoic acid (+63%) and bilirubin (+33%) as glucuronides. However, these increases were apparent only in the initial phase of excretion. In contrast, BHA markedly decreased (-43%) the biliary excretion of valproic acid glucuronides. Simultaneously, BHA increased the urinary excretion of the glucuronides of phenolphthalein (+48%), iopanoic acid (+450%) and valproic acid (+150%). A shift in the distribution of iopanoic acid and valproic acid and metabolites from liver to kidney was also apparent in BHA-fed mice. Thus, enhanced glucuronidation does not facilitate the biliary excretion of all glucuronidated compounds and only transiently increases others. It is likely that this phenomenon is the result of the glucuronides readily entering the plasma and being excreted by the kidney.

Animals↗
PubMed1988

Species variation in toxication and detoxication of acetaminophen in vivo: a comparative study of biliary and urinary excretion of acetaminophen metabolites.

Acetaminophen (AA) is converted to a toxic electrophile that may subsequently form a glutathione conjugate (AA-GS). In addition to the toxication pathway metabolites, which consist of AA-GS and its hydrolysis products (AA-cysteinylglycine, AA-cysteine and AA-mercapturate), detoxication pathway metabolites, such as AA-glucuronide and AA-sulfate, are also formed. In order to evaluate the role of these opposing pathways in the reported species variations in susceptibility to AA-induced liver injury, AA was administered to hamsters and mice, species which are susceptible to AA-induced liver injury, and to rats, rabbits and guinea pigs, species which are relatively resistant to AA-induced liver injury, and the biliary and urinary excretion of AA metabolites were measured simultaneously for 2 hr after administration of AA (1 mmol/kg i.v.). The AA-susceptible species excreted 27 to 42% of the dose as toxication pathway metabolites, whereas the resistant species excreted only 5 to 7% of the dose as toxication pathway metabolites. Most of the toxication pathway metabolites appeared in bile, where their composition reflected hepatic gamma-glutamyltranspeptidase activity; hamsters and mice (low gamma-glutamyltranspeptidase activity) excreted mainly AA-GS, whereas bile from rabbits and guinea pigs (high gamma-glutamyltranspeptidase activity) contained significant amounts of AA-GS hydrolysis products. Thus, the biliary excretion of AA-GS and its hydrolysis products may be used as an index of toxic activation of AA. The excretion of the detoxication pathway metabolites (AA-glucuronide and AA-sulfate) was 74, 62, 41, 27 and 12% of the dose in guinea pigs, rats, mice, rabbits and hamsters respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetaminophen↗
PubMed1987

Age-dependent biliary excretion of glutathione-related thiols in rats: role of gamma-glutamyltransferase.

The role of gamma-glutamyltransferase (GGT) in the biliary excretion of glutathione (GS) was studied in rats during postnatal development. Between 2 and 10 wk of age the biliary excretion of GS-related sulfur increased ninefold. During this period, alterations were observed in both hepatic GGT and the composition of GS-related thiols and disulfides in bile. For instance, between 3 and 4 wk of age, GGT activity and the biliary excretion of GS hydrolysis products (Cys-Gly and Cys) increased markedly, and the latter became the predominant sulfhydryls in bile. However, by 10 wk of age, the excretion rate of GS increased and exceeded the rate of excretion of Cys-Gly and Cys. The parallelism between hepatic GGT activity and the biliary excretion of GS-hydrolysis products during development suggests a role for GGT in the formation of biliary Cys-Gly and Cys. Furthermore, in 4-wk-old rats, inhibition of hepatic GGT by acivicin markedly decreased the biliary excretion of Cys-Gly and Cys and increased that of GS without influencing the excretion of total GS-related sulfur in bile. The biliary excretion of GS-related thiols was less responsive to acivicin in 2- and 7- to 10-wk-old rats, suggesting that GGT plays a smaller role in influencing biliary thiol composition at those ages. In summary, GS transported into bile is hydrolyzed in an age-dependent manner, however, the GGT-initiated hydrolysis of GS does not affect the biliary excretion of total thiols in rats.

Aging↗
PubMed1987

Effect of inhibition of gamma-glutamyltranspeptidase on biliary and urinary excretion of glutathione-derived thiols and methylmercury.

Acivicin (AT-125; 6.25-200 mumol/kg i.v.) inhibited hepatic, biliary and renal gamma-glutamyltranspeptidase (GGT) activity up to 88, 99 and 97%, respectively, in 4-week-old rats. This inhibition of GGT by acivicin resulted in a 10- to 12-fold increase in the biliary excretion of reduced (GSH) and oxidized glutathione. Because the biliary excretion of cysteinylglycine (Cys-Gly), Cys-Gly disulfide, cysteine (Cys) and cystine concomitantly decreased (63-99%), the biliary excretion rate of total glutathione-derived thiols and disulfides did not change. In contrast, acivicin treatment dramatically elevated the urinary excretion rate of glutathione-derived thiols in a dose-dependent fashion, resulting in a 390-fold increase at the highest dosage. This mainly originated from enhancement of urinary excretion of GSH (up to 7200-fold), although the excretion of Cys and Cys-Gly into urine was also increased. Acivicin treatment did not affect hepatic and renal levels of GSH but, at high dosages, reduced the concentration of Cys in these organs. GSH and oxidized glutathione concentrations in serum were increased, whereas cystine was diminished in acivicin-treated rats. Inhibition of GGT by acivicin (100 mumol/kg i.v.) failed to influence the biliary excretion of methylmercury but increased urinary excretion 34-fold. Even though the urinary thiol excretion was much higher than the biliary thiol excretion in the acivicin-treated rats, methylmercury was preferentially excreted into bile rather than urine, indicating the importance of the liver as an excretory organ for methylmercury.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Disposition of metals in rats: a comparative study of fecal, urinary, and biliary excretion and tissue distribution of eighteen metals.

Fecal (0-4 days), urinary (0-4 days), and biliary (0-2 hr) excretion and tissue distribution of 18 metals were examined in rats after iv administration. Total (fecal + urinary) excretion was relatively rapid (over 50% of dose in 4 days) for cobalt, silver, and manganese; was between 50 and 20% for copper, thallium, bismuth, lead, cesium, gold, zinc, mercury, selenium, and chromium; and was below 20% for arsenic, cadmium, iron methyl mercury, and tin. Feces was the predominant route of excretion for silver, manganese, copper, thallium, lead, zinc, cadmium, iron, and methyl mercury whereas urine was the predominant route of excretion for cobalt, cesium, gold, selenium, and chromium; while both excretion routes were equally important for bismuth, mercury, arsenic, and tin. Biliary excretion seems to be an important determinant for the fecal excretion of silver, arsenic, manganese, copper, selenium, cadmium, lead, bismuth, cobalt, and methyl mercury. Between 45 (silver) and 0.8% (methyl mercury) of the dosages administered of these metals was excreted into bile in 2 hr, and they exhibited high bile/plasma concentration ratios. The biliary excretion of copper, selenium, lead, and chromium did not increase proportionally with dosage, suggesting that the hepatobiliary transport of these metals is saturable. The fraction of dosage excreted into bile was independent of the dosage for silver, arsenic, manganese, bismuth, methyl mercury, mercury, gold, cesium, thallium, and tin, but markedly increased with increase in dosage of cadmium, cobalt, zinc, and iron. The latter phenomenon is probably due to saturation of hepatic (cadmium, zinc) or extrahepatic (iron) metal-binding sites. Comparison of biliary and fecal excretion rates indicates that arsenic and selenium undergo intestinal reabsorption, whereas thallium and zinc enter the feces also by non-biliary routes. Most of the metals reached the highest concentration in liver and kidney. However, there was no direct relationship between the distribution of metals to these excretory organs and their primary route of excretion.

Animals↗
PubMed1985

Age-development and inducibility of hepatic glutathione S-transferase activities in mice, rats, rabbits and guinea-pigs.

Hepatic glutathione S-transferase (GST) activities towards 1-chloro-3,4-dinitrobenzene (DNCB), 3,4-dichloronitrobenzene (DCNB), sulfobromophthalein (BSP), p-nitrobenzyl chloride (NBC), ethacrynic acid (EA), trans-4-phenyl-3-buten-2-one (TPBO) and 1,2-epoxy-3-(p-nitrophenoxy)propane (ENPP) were determined in mice, rats, rabbits and guinea-pigs during ageing and after pretreatment with enzyme inducers. Variations were observed in the developmental patterns and in the phenobarbital-, benzo(a)pyrene-, pregnenolone-16 alpha-carbonitrile-, butylated hydroxyanisole-, trans-stilbene oxide-inducibility of hepatic GST activities in the same species towards different substrates. For example, in rats GST activities for EA, DCNB and TPBO increased respectively, 2.3-, 4.8- and 25-fold during age-development, and after treatment with TSO 1.2-, 3.6- and 1.3-fold. Species differences were found in the maturation and in the inducibility of GST activities. For instance, GST activity toward EA at birth is mature in guinea pigs but not in the other species; phenobarbital treatment increased GST activities in mice and rats but not in rabbits and guinea-pigs; treatment with trans-stilbene oxide enhanced GST activity for TPBO 4.5-fold in mice but not at all in rats. It is concluded that hepatic glutathione conjugation exhibits functional heterogeneity which may be due to species dependent variations in the responsiveness of GST isoenzymes to endogenous and exogenous influences.

Aging↗